A high-resolution chronostratigraphy developed from a three-core transect in the Florida Keys shows that mixed carbonate/siliciclastic sediment distribution and deposition was controlled by a combination of sediment supply, eustasy, and variations in current intensity. Interaction of these three variables contributed to the complex lateral and vertical heterogenity of this mixed system.

A proposed mid-Oligocene (~29 Ma) eustatic lowstand obstructed current flow through the Gulf Trough across north Florida and likely aided in initiating a weak Loop Current in the Gaff of Mexico and terminated early Oligocene carbonate sedimentation. With restricted flow through the Trough, siliciclastic sediments eroding from the Appalachian Mountains to the north filled the Trough and began transport down the Florida peninsula through a fluvial-deltaic(?) system. The mixed facies in the upper and middle Keys overlie an 8.8 m.y. hiatus above the lower middle Miocene limestones with three phases of siliciclastic deposition during the late Miocene to Pliocene. The lower Keys did not receive siliciclastics but instead formed a laterally-equivalent fine-grained carbonate unit (Pliocene) after an 11.5 m.y. depositional hiatus.

We hypothesize that a combination of eustatic and regional (current) events played the primary role in determining the timing and lateral extent of siliciclastic deposition in south Florida. Infilling of the Gulf Trough and progressive restriction of the Isthmus of Panama increased the velocity of the Loop Current. Subsequently, eustatic fluctuations aided in transporting the coarse siliciclastics to southernmost Florida, and strong current flow through the Straits of Florida resulted in sediments prograding to the east.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas